Variable speed transmission



Dec. 2, 1941. o. LJUNGSTROM 2,264,444

VARIABLE SPEED TRANSMISSION Filed Nov. 5, 1937 8 Sheets-Sheet l INVENTOR BY fiiM ATTORN EY Dec. 2, 1941. o. LJUNGSTROM 2,264,444

I VARIABLE SPEED TRANSMISSION Filed Nov. 5, 1957 8 Shets-Sheet 2 INVENTOR BY Mix/W ATTORNEY Dec. 2, 1941. o. LJUNGSTROM VARIABLE SPEED TRANSMISSION 8 Sheets-Sheet 3 Filed Nov. 5, 1957 INVENTOR I Q. Ljungsh-em ATTORNEY 1941- o. LJUNGSTROM 2,264,444

VARIABLE SPEED TRANSMISSION Filed Nov. 5, 1937 8 eets-Sheet 4 INVENTOR BY 0. Ljun s/rQ/r) ATTORNEY Dec. 2, 1941. o. LJUNGSTROM 2,264,444

' VARIABLE SPEED TRANSMISSION Filed 1937 8 Sheets-Sheet 5 1 1 x {9 6e 8 f 9/1 9 l/ I A Y Q Q Q lie I g I "7 k 7 INVENTOR O Ljungsfram ATTORNEY Dec; 2, 1941. 0. LJUNGSTROM 2,264,444

VARIABLE SPEED TRANSMISSION 7 Filed Nov. 5, 1937 8 sheets sheet 6 a a-mrlelvmvr stcGNOIDY INVENTOR O. Ljuhg sfrom w muuf ATTORNEY I Dec. 2-, 1941. O, L UNGSTROM 2,264,444

VARIABLE SPEED TRANSMISSION Filed NOV. 5, 1937 8 sheets sheet 7 mig. Z5.

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VARIABLE SPEED TRANSMISSION Filed Nov. 8 Sheets-Sheet 8 :lnferna/ Gear of in RAM.

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INVENTOR O. Ljungsh-am BY 021,4 6M

ATTORNEY Patented Dec. 2, 1941 UNITED STATES PATENT OFFICE 2,264,444 VARIABLE SPEED TRANSMISSION Olof Ljungstrom, Detroit, Mich.

Application November 5, 1937, Serial No. 173,027

17 Claims.

My invention relates to a variable speed transmission, and in particular to a transmission of the hydraulic .type for producing a smooth and continuous change in the drive ratio.

An object of the invention is to devise a variable speed transmission suitable for use on motor vehicles and in which the drive ratio between the engine shaft and thedriven shaft is automatically controlled to obtain best eiiiciency of the operation of the engine.

Another object is to devise a variable speed transmission in which the drive ratio is auto matically varied to meet the torque requirements of the load.

A further object of my invention is to devise a variable speed transmission which may be embodied in the axle construction of a motor vehicle displacement hydraulic pump, and another novel feature of my invention is embodied in a simplifled construction of a servo-motor for varying the displacement of the pump. J

Additional objects are to provide novel means for controlling the servo-motor; to provide novel means for interlocking the engine accelerator control and the transmission control; and to provide novel means for replenishing the fluid in the fluid transmission circuit. v A preferred embodiment of my invention is illustrated in the accompanying drawings in which:

Figure 1 is a longitudinal sectional view of the transmission taken'along the line l'! of Figure 2;

Figure 2 is a transverse sectional along line 2-2 of Figure 1;

Figure 3 is a sectional. view taken along line 3-3 of Figure 1 showing the arrangement of one ofthe secondary hydraulic units;

Figure 4 is a sectional view taken alongline 4-4 of Figure 2 showing the arrangement of the primary lwdraulic unit, the servo-motor and the control arrangement therefor;

5-5 of Figure 4 showing the details of the presview taken housing provided with a supporting .flange la sure responsive element for controlling the displacement of the primary pump;

Figure 6 is a fragmentary sectional view taken along the cutting line 5-6 of Figure 1 showing a horizontal section through one of the secondary hydraulic units, and the details of one of the control valves;

Figure 7 is a sectional view taken along line l-l-of Figure 1 showing the arrangement of two control pumps; i

Figure 8v is a sectional view taken along line 8-8 of Figure 4 showing the arrangement of the control ducts;

Figures 9a, 9b and 9c are views illustrating the construction of the control lever;

Figures 10, 11, 12; 13 and 14 are schematic transmission system for difierent car speeds and for difierent engine speeds.

Referring to the drawings, l indicates a ma which is preferably bolted directly to the engine block or other suitable support carried by the frame of the car. worm 2, preferably of the hourglass type, is'journaled in' the housing concentric with the flange la and is driven from the engine shaft by means of a flange coupling 3 adapted to! be bolted to a corresponding flange naled'on an axis transversely of. the axis of the """l igure}5is aisectional view-taken along-line worm. The worm 2. is also arranged to drive the rotor element 5 of. a primary hydraulic unit which sometimes acts as a pump and at other times acts as a motor. The rotor 5 is preferably mounted upon a hollow shaft 5a which is journaled atone end by roller bearing 6a mounted in casing I and at the other end by roller bearing 6b mounted in an end plate lb secured to casing I on the opposite side of the casing from flange Ia and forming one end wall of the primary pump housing. Worm 2 is preferably formed ona'hola sleeve b on shaft 512, and also has a splined connection with a shaft 2b mounted within the worm 2, the shaft 2b being journaled in casing I by a ball bearing '60. The other end of shaft 2b is supported within shaft Ed by means of a sleeve 20 which is provided with a shoulder abutting the end of the shaft 2a, and a nut 2d threaded onto the reduced end of shaft 2b cooperates with the sleeve 20 in clamping the worm shaft 2d and the inner race of ball bearing 60 onto the shaft 2b.

A resilient coupling is provided between the driving flange 3 and the worm 2 to absorb vibrations, and this coupling consists of a sleeve I having a splined connection with the stub shaft 3a of flange 3 and also having a. circular plate flange 1a mounted within a housing carried by the end of worm shaft 2b and formed of a radial flange 2e on the end of shaft 2b and a cooperating annular flange 21 secured to the flange 2e. The flange la is coupled to the-housing formed of flanges 2e and 2; by resilient coupling devices comprising a series of short helical springs lb located in recesses or holes formed in the flange Ia and extending into recesses formed in the flanges 2e and 2f, the arrangement being such that the driving torque is transmitted through the springs 'lb. The sleeve I is journaled in a cover plate Ic mounted in the end of the flange Ia. It will be understood that any other form of vibration absorbing device may be employed if desired.

A cap or cover Ie is bolted to end plate lb and encloses the roller bearing 6b. This cap is provided with a duct Da which communicates at one end with the fluid passage of the primary pump 5 and supplies lubricating fluid to the worm 2 by means of a hollow stem Ic extending into a central opening in the end of worm shaft 2b. The shaft 2b is provided with suitable ducts for conducting lubricant to worm 2. A duct Db extends from the lower part of cap Ic through the plate lb and returns excess oil or lubricant from cap lc to the oil sump located in the bottom of casing I.

The worm gear 4 is mounted between opposing ends of two sleeve elements 4a and 4a which are journaled in axial alignment with each other by means of ball bearings 6d and 6d mounted in sleeve extensions of housing plates Id and Id respectively. Each of the sleeves 4a and 4a is provided with internal gear teeth (4?) and 4b) forming the ring gear of a differential gearing. Since the transmission is symmetrical on each side of the vertical central axis shown in Figure 1 of the drawings, the construction will be described for the right-hand side only, and it will be understood that the construction on the other side is identical, corresponding elements on the left side being identified by the same reference characters primed.

The outer face of the cover plate Id is provided with a circular recess forming the casing for the rotor 8 of a secondary hydraulic unit.

' Rotor 8 is mounted upon a hollow shaft Batvhich in turn is journaled at one end' by ball bearings 6e and at the other end by ball bearings 6fmounted in the plate Ie bolted to plate Id. The inner end of the shaft 8a is provided with gear teeth 8b forming the pinion gear of a differential gearing. A hollow shaft 9 is arranged withlow shaft 2a which has a splined connection with other ring I0 of the spider is supported from the flange 9a by a series of arms Illa bolted to the flange 9a. Three planet gears Ila, Ill) and Ilc are journaled by needle bearings upon three hollow shafts I2a, I2b and I2c supported between the rings 9a and I0 forming the planet spider. The inner end of shaft 9 is maintained concentric with the inner end of shaft Ba by sleeve 9b. The outer end of shaft 9 is journaled in a ringbearing 90 supported by radial arms from plate If bolted to the plate Ie, and the outer end of the shaft 9 has a splined connection with the sleeve 9d which is journaled in the cap member lg by ball bearings So. The sleeve 9d is provided with a coupling flange So to which one of the traction wheels of the vehicle may be connected by any suitable connection. The sleeve 9d is maintained in position on the shaft 9 by means of a nut 91 threaded on the end of the shaft 9.

As shown in Figure 6, the sleeve bearing 9c is provided with an oil groove on the inner face thereof, and lubricant for this hearing is supplied from the hydraulic circuit of pump 8 through a duct Dc which passes through the plate Ia and through one of the radial arms which supports the bearing 90 on the plate I). Any excess lubricant which collects in the cap lg is returned to the oil sump in the bottom of the housing I through duct Dd, see Figure 1. Shaft 9 is closed at both ends by resilient discs 9g and Sn, and oil is admitted to the shaft through holes 970 communicating with the oil groove in'bearing 9c, and oil is supplied from the shaft 9 to the gear 81) and to the interior of the hollow journal shafts I2a, IZb and I2c through suitable ducts as shown in Figure 1. Oil ducts are also provided in hollow journal shafts I2a, I2b and I2c for supplying lubricant to the needle bearings of the planet gears. I

, The primary pump 5 is a variable displacement pump, and in the construction shown, the rotor 5 with the slidable vanes 50 are mounted for rotation in a circulu'recess formed in a sliding liner 5d, the liner being arranged for sliding movement so that the displacement of the pump may be varied from a maximum on one sideof the pump axis as shown in Figure 4 to a maximumon the other side of the pump axis. In other words, by shifting the liner 5d from the position shown in Figure 4 to the right, the displacement of the pump can be varied from a maximum down to zero and to a maximum in the opposite direction, thus reversing the direction of flow of the fluid without reversing the direction of rotation. The sliding vanes 50 are held in position by suitable rings 5d engaging shoulders formed on the ends of the vanes as shown in Figure 2, and these vanes may also be urged outwardly by suitable springs as shown in the construction illustrated in Figure 3 for the secondary pump 8. secondary pump units is substantially like that of the primary unit except that the displacement is not variable, and the construction is shown in Figure 3 where the rotor 8 is provided with slidmg vanes 80 which are urged outwardly by springs 8d. Secondary pump 8 has the same construction as pump 8'.

in the shaft 8a and is provided with a circular flange 9a on the inner end thereof, which flange forms one ring of a spider for supporting the planet gears of the differential gearing. The

The hydraulic circuit between the primary and the two secondary pump units includes a duct H which connects with the port formed in the upper part of the liner 5d and runs forward within the casing I towards flange Ia, and divides into two passages, the passage Ha extend- The construction of the '5 and communicating with the port in the lower side of liner d. In a similar manner,.the fluid circuit for pump unit 8' is completed by a duct Hb' extending from the opposite side of the rotor 8' back to the primary unit 5 and communicates with the port formed'in the lower part of liner 5d. Thus both pump units 8 and I may be driven from the primary pump 5 or either.

secondary unit may drive the primary pump. Also, fluid from one secondary pump may circulate through the other secondary pump without passing through the primary pump.

Any loss of fluid from the fluid circuit conmeeting the various hydraulic units is replenished by means of a. make-up pump driven'from the worm gear 4 and operating to draw fluid from the sump in the base of the transmission and to introduce it in the low pressure side of the circuit. The make-up pump is embodied in a double pump construction which also suppliesfluid to control and operate the displacement varying means of the primary pump 5. The make-1111 and control pumps are enclosed in a casing I3 secured to the bottom wall of the casing I below the sump, and the driving unit of both pumps comprises a gear I3a mounted on a shaft I3b driven from worm gear 6 by pinion I,3c. The makeup pump comprises a gear Ii meshing with driven gear 13a. The suction side Its of the make-up pump communicates with the sump and draws fluid therefrom, while the output side Mp of the pump supplies fluid through-duct Ida to space lob located in the casing I adjacent the rotor 5. From space Mb fluid issupplied to either side of the fluid circuit of pump 5 through spring pressed valves Ito and Md, depending upon which side is the lowpressure side of pump 5. The valves Mo and ltd are provided to prevent th flow of fluid from the high pressure side of the fluid circuit to the low. pressure side, and also prevent back-flow into the make-up pump. The. make-up pump is provided with a pressure regu-' lating valve connected to its outlet side and consisting of a cylinder Me communicating with the pump outlet and provided with a relief aperture I4 which is normally closed by means of a spring pressed piston located in the cylinder Me. A screw for adjusting th pressure in the delivery side of the make-up pump is located within the removable cap Hg. The construction of the pressure regulating. valve for the make-up pump is the same as for the valve of the control pump which is shown in detail in Figure 6 of the drawings.

The control pump for supplying fluid to the servo-motor for operating the liner 5d of the primary pump consists of a gear I5 meshing with the driven gear I 3d. The inlet side I53 of the, control pump communicates with the sump and draws fluid from the sump, while the outlet lip 01 the pump supplies fluid through duct lid to the control valve of the servo-motor. The control pump is provided with a pressure regulating pressure of the spring I5e upon the piston I Id.

may be adjusted by screw I5! located on the outside of the casing I andprovided with a cover cap I 59.

In varying the position of the liner Ed, I utilize the liner as a power piston in the servo-motor construction by introducing fluid under pressure to the space on one side or the other of the liner. The control valve for supplying fluid to the spaces on opposite sides of the liner is embodied in the housing or cylinder I6 bolted to the casing I and illustrated in section in Figure 4. The cutting plane for the section through the cylinder It in Figure 4 is shown by the line 1- -4 in Figure 8. One element of the control valve consists of a sleeve I! mounted in cylinder l6, the sleeve I'l being connected to and movable with the liner 5d by a stem I111. The inner wall of the cylinderv I6 is provided .with a circular port Ifia surrounding the sleeve II and is supplied with fluid from the control pump through duct -I5a. Sleeve I1 is provided with an aperture I lb which communicates with the circular port Ilia to admit 'fluid under pressure to the inside of the sleeve Il. Cylinder I6 is also provided with a circular port I6b surrounding the sleeve I1, and this port is connected by duct I60 to the space ie located between the right-hand side of the liner 5d and between the left side of liner 5d and its casing.

The spaces at'the ends of sleeve I] within cylinder l6 are connected with the sump in housing I by duct lBf.

A valve rod I8 is arranged within the sleeve I7 and is provided with a disc'valve I8a arranged so that its peripheral edge. covers the apertures in sleeve I! to cut off communication between the circular port I I6!) and the interior of the sleeve IT. A second disk valve element llib is carried by. the rod l8 and is arranged so its peripheral edge covers the apertures which connect the circular port ltd with the interior of the sleeve IT. The rod I8 is biased towards the left by means of spring I located in housing l9 secured to cylinder It, but movement of the rod is limited by means of the member 20 having threaded engagement with the left end of the rodl8 and provided with a roller 20a. engaging As shown in Figure 9c, the cam surface on the lower end of thecontrol lever 2| is formed of three sections, the first section 2la corresponding to the neutral position of the transmission, the second section 2 lb corresponding to the position for forward operation, and the third section 2 lo corresponding to the position of the lever for reverse operation. When the lever 2| is in neutral position, the cam roller 20a rests against thecam section 2Ia and the liner id is held-in such position that the output of pump 5 is sumcient to rotate secondary pumps 8 and 8' in the proper direction and at the proper speed to hold the driven shafts 9 and :9 stationary. This condition of operation is indicated diagrammatically in Figures 11 and 11a.

In Figure 15, I have illustrated a preferred arrangement for operating the control'leverfl from the accelerator pedal of the motor vehicle. In this arrangement, the accelerator pedal 2;

is pivotally supported upon a bracket 22a mounted on the floor-boards of the vehicle, and the arm 22b of the pedal is connected by a link 220 to the lower end of lever 23 pivoted intermediate its ends to the bracket 22a. The lever 23 is provided with an arcuate slot 23a having its center of curvature located at the upper end of control lever 2|, and the lever 2| is operated from the lever 23 by link 23b pivotally secured to the upper end of lever 2| and having pivotal connection with a sliding block 230 arranged in arcuate slot 234;. The engine throttle 24 is operated by means of a connection from the upper end of lever 23. This connection consists of two link parts 24a and 24b joined by a compressible section consisting of a cylinder 24c carried by link 24b and receiving the end of link 24a and also having telescopic engagement with a cylinder 24d carried by link 24a. A compression spring 24e is arranged within cylinder 24d and acts to normally hold the links 24a and 24b in extended position.

With the arrangement shown in Figure 15, when the accelerator pedal 22 is in idling position, the control lever 2| is maintained in neutral position, and depression of the pedal 22 will operate to open the engine throttle and to shift control lever 2| to the position for forward operation. For reverse operation, the link 23b must be shifted to a position adjacent the upper end of the lever 23, and, for this purpose a button 25 is provided on the dashboard of the vehicle, and by pulling this button out, the link 23b is shifted to the upper position through bell crank 25a and link 25b. In this position the lever 2| will be rotated in the opposite direction fromthe direction of operation for the position shown in Figure 15 when pedal 22 is depressed.

When it is desired to operate the transmission for forward drive, the control parts are as shown in Figure 15. Depression of accelerator pedal 22 moves the lever 2| so that the cam roller 20a begins to bear upon the inclined cam surface 2|b, and at the same time the engine throttle being opened through the connection 24a24b. As soon as the cam roller 20a. starts down the cam surface 2|b, the spring |8c moves the valve rod l8 to the left of the neutral position (see Fig. 4 whereby the valve disc Ilia uncovers ports in sleeve I! to admit fluid under pressure from the interior of sleeve ll to circular port I61), and from this port through duct I60 pump 5, so the pump 5 acts as a load on the secondary pumps and imposes a reaction on the floating elements of the two differential gears. This reaction causes a torque to be applied to the two drive shafts 9 and 9', and the vehicle will be driven in a forward direction at a definite speed, depending upon the engine speed and the position of the control lever 2|.

As the accelerator pedal 22 is further depressed, the lever 2| will cause the further shifting of the liner 5d until the liner becomes concentric with the rotor 5 and the output of the pump 5 becomes zero. In this position the two secondary pump units will be held in stationary position, and this condition of operation is indicated in Figures 12 and 12a.

Further movement of the accelerator pedal causes the liner lid to shift to the opposite side of the pump axis and reverses the direction of flow of fluid through pump 5, as shown in Figure 13. Under this condition of operation, the pump 5 acts as a pump to supply fluid under pressure for driving the secondary pump units in the opposite direction of rotation, and, as shown in Figure 13a, under this condition of operation all elements of the differential gears rotate in the same direction. When the speed of rotation of the secondary rotors becomes equal to the speed of rotation'of the worm gear 4, a condition of direct drive is obtained, that is,

, the drive ratio is the ratio between worm 2 and worm gear 4.

Further depression of pedal 22 causes shifting of the liner to the left until a maximum displacement of the pump 5 is obtained as shown in Figure 14, thus increasing the speed of rotation of sun gear 8b in the direction shown in Figure 14a, and maximum forward drive is obtained.

From the foregoing it will be seen that as the accelerator pedal is moved from idling position to fully operated position during forward operation, the secondary pumps 8 and 8 first supply fluid under pressure to the primary pump, tending to drive thepriingry pump in the same direction of rotation an adding a certain amount of torque to the engine torque applied to the worm gear 4. As the vehicle accelerates, the speed of rotation of the secondary pumps decreases until they come to a stop and then the primary pump begins to drive the secondary pumps in the opposite direction of rotation,

to the space 5e to the right of the liner 5d. At

the same time, valve disc |8b uncovers ports in sleeve H to permit fluid to flow from the space 5 on the left of liner 511 through duct Hie, through the right end of sleeve l1, and through exhaust duct I6 back to the sump in casing The pressure exerted in the space 5e against the liner 5d causes the liner to move to the left, and this movement causes the displacement of pump 5 to be decreased, as shown by the positions of the liner in Figures 11 and 12. Movement of the liner also causes movement of the sleeve to the left to close the ports in the sleeve H by the valve discs |8u and lab and thus maintain the liner in a definite position depending upon the position of the lever 2 It will be understood thereby adding their speed of rotation to the speed of the worm gear 4 in driving the driven shafts 9 and 9. It will thus be seen that dur ing the first stage of acceleration the second pumps drive the primary pump as a motor, and during the later stage of acceleration, the function of the hydraulic unit is reversed and the that the servo-motor construction'causes the liner 5d to follow the movement of the valve rod l8 in either direction from neutral position.

Since the displacement of the pump 5 has been reduced from the displacement in the neutral position, the output of the secondary pumps 8 and 8' becomes greater than the intake of the primary pumpdrives the secondary pumps as motors in the opposite direction of rotation.

For reverse operation, the button 25 on the dashboard is pulled, out, thereby shifting the link 232) from the lower position on lever 23 to the upper position. Depression of the accelerator pedal 22 will, under this condition, open the throttle to the engine and operate the lever 2| in reverse direction from that for forward operation and cause movement of the pump liner 5a to the right from the neutral position, as shown in Figure 10. This movement increases the displacement of the primary pump which acts to drive the rotors of the secondary pumps at increased speed in the directions indicated in Figure 10a and at a greater speed than the speed of the ring gears of the differentials, thus causing movement of the vehicle in reverse direction.

The cam surface on the lever 2| may be so designed that the engine throttle becomes substantially fully open before the lever is moved beyond the neutral section 2| a of the cam surface, and further movement of the control lever is made possible by the provision of the compressible link consisting of the elements 240, Nd, and 24e in the connection to the engine throttle. It will be understood, however, that the arrangement may be such that the neutral cam section 2; is of small extent and the engine throttle is gradually opened as the control leveris moved to either side of the neutral position into the forward or reverse sections 2) and 2 la.

The transmission may be operated as described above without any automatic control, but I- prefer to provide automatic control ofthe transmission ratio in accordance with the load demands,

and for this purpose, I provide means for controlling the position of the valve rod 18 in accordance with the pressure developed in the main hydraulic circuit. 'One form of automatic control arrangement is shown in Figures 4 and 5, and includes a pinion 26 mounted in casing I9 and having splined engagement with valve rod I8. Mounted within the casing I91; and supported on housing I9 is a fluid cylinder 21 which is supplied with fluid under pressure'from the main hydraulic circuit through pipe 21a. The pipe 21a should connect to the high pressure side of pump, 5 for-forward operation. A piston 21b is arranged in the cylinder 21 and carries a rack 270 which engages the pinion 26. Thepiston 27b and the rack 210 are normally biased to thelower position by means of a spring 21d surrounding a sleeve 21c secured to piston 21?).

So long as; the pressure in the main hydraulic circuit does not exceed a value sufficient to overcome spring 21d, the piston 21b remains in its' lowermost position, and the transmission is controlled entirely by the movement of the lever 2|. Should the pressure in the hydraulic circuit increase above the value necessary to overcome the force of the spring 21d,'the piston 2112 will rise until the force of the spring equals the fluid pressure, and in rising the rack 210 will rotate the pinion 28 on the valve rod l8, and will thereby cause the valve rod to rotate in such direction that the threaded end thereof is partially unscrewed from the member 20, which results in a movement of the valve rod l8 to the right as viewed in Figure 4. This movement of the valve rod is in such direction that it will bring about a change in the displacement of pump 5 which will cause a reduction in the pressure developed in the main hydraulic circuit. It will thus, be seen that the action of the automatic control is to prevent excessive pressures from being developed in the hydraulic circuit and to prevent a too rapid change in the drive ratio.

The automatic control is efiective at any stage of forward operation. It normally tends to increase the ratio between the speed of the pro-' peller shaft and'the speed of the driven shafts 9 and 9', but whenever the vehicle meets with increased resistance, such as results from ascending a hill, the increased pressure in the fluid circuit operates through the automatic control to vehicle from standstill, if the accelerator pedal is depressed quickly to its fully operated position,

the pressure developed in the fluid circuit may be suflicient to operate the piston 27b to its uppermost position, and, as the vehicle accelerates and the fluid pressure decreases, the drive ratio will be automatically increased.

In Figure 16, I have shown a modified arrangement for controlling the transmission from the accelerator pedal. This arrangementdiifers from Figure 15 in that the lever 2| is controlled directly from the pedal 22 by link 22d, and the lever 23 with the arcuate slot is controlled from -in Figure 16, depression of the pedal 22 causes shifting of the lever 2i for forward operation and also opens the engine throttle; For reverse operation, the pedal 22 is depressed at the heel portion, thereby causing lever 2! to move in the opposite direction, and, in order to have-this movement open the engine throttle, it is necessary to first pull out the button 25 to shift the connection 240 to the bottom end of the lever 23. I

prefer the arrangement illustrated in Figure 15,

since by adjusting the button 25 so the sliding block 230 is adjacent the pivot point of the lever 23, it is possible to control the engine without movement of the transmission control-lever 2|.

As applied to a motor vehicle in the manner shown in Figures 15 and 16, my invention provides a variable speed transmission which is controlled entirely from the accelerator pedal of the vehicle, and the usual change speed gear and clutch elements are dispensed with. Also, my variable speed transmission embodies a differential drive which permits the two driven shafts to rotate at different speeds when the vehicle is passing around a curve. This is made possible by reason of the fact that the transmission fluid may circulate between the two secondary pumps without. passing through the primary pump.

The threaded engagement between the end of valve rod I8 and the member 20, and the cooperation between the cam surface on the lower end of lever 2| with the sliding member 20 constitutes an adjustable stop for limiting the movement of the valve rod l8 under the action of biasing spring I80, and this stop is under the separate and joint control of the lever l8 and the pressure existing in the fluid circuit of the primary pump through the action of piston 21b driving the pinion 26. Also, the threaded engagement between the'end of valve rod l8 and the stop element 20 constitutes an expandible 'connection which is normally held in retracted position by the spring 21d, but is. expanded under the action of the fluid pressure in the main hydraulic the engine or to'the motor vehicle frame, it will decrease the ratio between thespeed'of the propeller shaft and the speed of the driven shafts,

thus increasing the driving torque to accommodate the increased load. Also, in accelerating the -with respect to the .traction wheels.

be understood that the shafts 9 and 9' will be connected to the traction wheels of the vehicle by means of universal joints" and short driven shafts to permit movement ofthe vehicle frame In this manner the unsprung weight of the vehicle is reduced to a minimum. I

The term convertible pump as employed herein denotes a pump which will operate either as a fluid pump or as a fluid motor. The term reversible displacement" denotes that the displacement may be changed to reverse the direction of flow of fluid during pump operation without reversing the direction of rotation, or, for motor operation, to reverse the direction of rotation without reversing the flow in the fluid circuit.

I have herein described the principle of my invention and illustrated a preferred embodiment thereof. Certain modifications have been pointed out to indicate the broad scope of the invention. Various other modifications will occur to those skilled in the art, and I desire it to be understood that all modifications which fall within the terms of the appended claims are to be considered as falling within the scopeof my invention.

What I claim is:

1. A variable speed transmission system comprising a pair of differential gear sets, a common drive shaft for driving one element of each differential gear set, a pair of driven shafts connected respectively to a second element of said differential gear sets, a pair of convertible hydraulic pumps connected respectively to the third element of said differential gear sets, and a variable displacement hydraulic pump driven by said drive shaft and connected in parallel fluid circuit relationwith said pair of convertible hydraulic pumps.

2. A variable speed transmission system comprising a pair of differential gear sets, a common drive shaft for driving ,one element of each differential gear set, a pair of driven shafts connected respectively to a second element of said differential gear sets, and variable speed driving connections between said drive shaft and the third element of each differential gear set, said driving connectionsbeing interconnected thereby said driven shafts are driven in differential speed relation.

3. A transmission comprising a pair of differential gear sets, a pair of driven shafts connected respectively to one element of said gear sets. a drive shaft arranged to drive a second element of each of said gear sets, a pair of fluid pumps driven respectively by the third element of said gear sets, said fluid pumps being connected in series fluid circuit relation whereby said driven shafts are connected in differential speed relation.

4. A variable speed transmission comprising, a

pair of differential gear sets, a pair of driven shafts connected respectively to one element of said gear sets, a drive shaft arranged to drive a second element of each of said gear sets, a pair of secondary fluid pumps driven respectively by the third element of said gear sets, said fluid pumps being connected in series fluid circuit relation whereby said driven shafts are connected in differential speed relation, a primary fluid pump driven by said drive shaft and connected in parallel fluid circuit relation with said secondary pumps, and means for varyingand reversing the displacement of said primary pump whereby to drive said pair ofv pumps in either direction and at variable speeds.

5. A transmission comprising a housing, a pair of driven shafts journaled in said housing in axial alignment, a pair of differential gear sets mounted in said housing, said driven shafts being connected respectively to the planet spiders of said gear sets, a drive shaft journaled in said housing and arranged to drive the ring gear of each of said gear sets, the sun gears of said gear sets being provided with hollow shaft extensions arranged respectively around said driven shafts. a pair of secondary fluid pumps having rotors mounted respectively upon said hollow shafts, said fluid pumps being connected in series fluid circuit,relation whereby said driven shafts are connected in differential speed relation, a primary fluid pump driven by said drive shaft and connected in parallel fluid circuit relation with said secondary pumps, and means for varyin and reversing the displacement of said primary pump whereby to drive said secondary pumps in either direction.

6. A variable speed transmission system comprising a pair of differential gear sets, a common drive shaft for driving one element of each differential gear set, a pair of driven shafts connected respectively to a second element of said differential gears sets, a pair of convertible hydraulic pumps connected respectively to the third element of said differential gear sets, a third convertible hydraulic pump drivenby said drive shaft and connected in parallel fluid circuit relation with said pair-of convertible hydraulic pumps, a make-up pump, ducts for supplying fluid from said make-up pump to said fluid circuit on. both sides of said third hydraulic pump, and check valves arranged in said ducts for preventing fluid from flowing from the high pressure to the low pressure side of said circuitwhile permitting fluid to flow from said make-up pump to the low pressure side of said circuit.

1. In a transmission system, the combination of a drive shaft, a fluid pump driven bysaid drive shaft, a driven shaft, a second fluid pump mechanically connected to said driven shaft and connected in fluid circuit with said first pump, a make-up pump, supply ducts for supplying fluid from said make-up pump to said fluid circuit on both sides of said first pump, and check valves arranged in said supply ducts for preventing fluid from flowing from the high pressure side of said fluid circuit back into said make-up pump.

8. A power transmission system comprising a drive shaft, a driven shaft, a fluid pump driven by said drive shaft, a second fluid pump, a fluid circuit connecting said pumps, means interconnecting said pumps whereby during one stage of operation one side of said circuit is at high pressure and during another stage of operation the other side of said circuit is at high pressure, a make-up pump and ducts for supplying'fluid to both sides of said fluid circuit from said make-up pump, and check valves arranged in said supply ducts for preventing fluid from flowing from the high pressure side to the low pressure side of said circuit while permitting fluid to flow from said make-up pump to the 'low pressure side of said circuit.

9. A variable speed transmission comprising, a pair of differential gear sets, a pair of driven shafts connected respectively to one elementof said gear sets, a drive shaft arranged to drive a second element of each of said gear sets, a pair of secondary fluid pumps driven respectively by the third element of said gear sets, said fluid pumps being connected in series fluid circuit relation whereby said drivenshafts are connected in differential speed relation, a primary fluid pump driven by said drive shaft and connected in parallel fluid circuit relation with said secondary pumps, means for varying the displacement of said primary pump to drive said secondary outlet pressure developed pumps in a given direction, and means responsive to the fluid pressure in said fluid circuit for controlling said displacement varying means.

10. A variable speed transmission comprising, a pair of differential gear sets, a pair of driven shafts connected respectively to one element of said gear sets, adrive shaft arranged to drive a second element of eachof said gear sets, a pair of secondary fluid pumps driven respectively by the third element of said gear sets, said fluid pumps being connected in series fluid circuit relation whereby said driven shafts are connected in differential speed relation, a primary fluid pump driven by said drive shaft and connected in parallel fluid circuit relation with said secondary pumps, said primary pump comprising a casing, a rotor mounted therein and a slidable liner surrounding said rotor for varying the displace-, ment of said pump, a source of fluid under pressure, ducts for supplying fluid from said source to the spaces within said casing on opposite sides of said liner, a valve for'controlling said ducts comprising two cooperating movable parts, one of said valve parts being arranged to supply fluid to the space on one side of said liner when moved in one direction and to supply fluid to the space on the other side of the .liner when moved in the opposite direction, and the said second mov able part of said valve being connected to and movable with said liner and arranged to cut off the supply of fluid when said liner reaches a predetermined position with respect to the first movable valve p'art, biasing means tending to move the first valve part in a direction to increase the pump displacement, a stop for limiting the movement of said first valve part by said biasing means, and means responsive to increase in the ing said stop in a direction to decrease the pump displacement.

11. A variable speed transmission comprising, a pair of diirerential gear sets, a pair of driven shafts connected respectively to one element of said gear sets, a drive shaft arranged to drive a second element of each of said gear sets, a pair of secondary fluid pumps driven respectively by the third element of said gear sets, said fluid pumps being connected in series fluid circuit relation whereby said driven shafts are connected in differential speed relation, a primary 'fluid pump driven by said drive shaft and connected in parallel fluid circuit relation with said secondary pumps, means for varying and reversing the displacement of said primary pump whereby to drive said pair of pumps in either direction and at variable speed, an engine fordriving said drive shaft, an accelerator for varying the speed of said engine, means for normally maintaining said displacement varying means in a position to prevent the transmission of power to said driven shafts, and a connection for operating said displacement varying means from said accelerator.

, 12. A variable speed transmission comprising, a pair of differential gear sets, a pair of driven shafts connected respectively to one element of said gear sets, a driv shaft arranged to drive a second element of each of said gear sets, a pair of secondary fluid pumps {driven respectively by the third element of said gear sets, said fluid pumps being connected in series 'fluid circuit re- 'lation whereby said driven shafts are connected in differential speed relation, a primary fluid pump driven by said drive shaft and connected in parallel fluid circuit relation with said secby saidpump for shiftsecondary pumps,

said displacement varying means in a position to prevent the transmission of power to said driven shafts, and a connection for operating said displacement varying means in one direction upon movement of said accelerator from idling position, said connection including means for at will reversing the direction of operation of said displacement varying means when said accelerator is moved from idling position.

13. A variable speed transmission comprising, a pair of differential gear sets, a pair of driven shafts connected respectively to one element of said gear sets, a drive shaft arranged to drive a second element of each of said gear sets, a pair of secondary fluid pump driven respectively by the third' element of said gear sets, said fluid pumps being connected in series fluid circuit relation whereby said driven shafts are connected in differential speed relation,'a primary fluid pump driven by said drive shaft and connected in parallel fluid circuit relation with said means for varying and reversing the displacement of said primary pump whereby to drive said pair of pumps in either direction and at variable speed, an engine for driving said drive shaft, an accelerator for varying the speed of said engine, means for normally maintaining said displacement varying means in a position to prevent the transmission of power to said driven shafts, a connection for operating said displacement varying means from said accelerator, and means responsive to pressure variations in the fluid circuit of said primary pump for modifying the control of said displacement varying means by said accelerator.

14. A variable speed transmission system comprising an engine having a drive shaft, an accelerator for varying the speed of said engine, a driven shaft, a variable ratio transmission means connecting said 'riven shaft with said drive-shaft, means for nor ally maintaining the control element of said transmission means in a position to prevent the transmission of power to said driven shaft, and means controlled by operation of said accelerator beyond fully open position for controlling said transmission means to initially apply power to said driven shaft and to increase the ratio of drive shaft speed to engine speed as the accelerator is moved beyond fully open position.

15. A variable speed transmission system comprising an engine having a drive shaft, an accelerator for varying the speed of said engine, a driven shaft, a variable ratio transmission means connecting said. driven shaft with said drive shaft, means for normally maintaining the con trol element of said transmission means in a position to prevent the transmission of power to said driven shaft, and means controlled by operation of said accelerator beyond fully open position for controlling said transmission means to apply power to said driven shaft, and means responsive to the load on said driven shaft for modifying the control of saidtransmission means.

16. A variable speed transmission system comprising an engine having a drive shaft, an accelerator for varying the speed of said engine, a driven shaft, a variable-ratio transmission means connecting said driven shaft with said drive shaft, said transmission means including a control element movable in one direction for forward operation and in the opposite direction for reverse operation, means for normally maintaining the control element in neutral position, a connection foroperating said control element in one direction by movement of said acceleratorfrom idling position towards accelerating position, said connection including means for at will reversing the direction of operation of said control element when said accelerator is moved from idling position in the same direction.

17. A variable speed transmission system comprising, a pair of diiferential gear sets, a pair of driven shafts connected respectively to one element of said gear sets, a driv shaft arranged to drive a second element of each of said gear sets, a pair of secondary fluid pumps driven respectively by the third element of said gear sets, said fluid pumps being connected in series fluid circuit relation whereby said driven shafts are connected in difierential speed relation, a primary fluid pump driven by said drive shaft and connected in parallel fluid circuit relation with said secondary pumps, said primary pump comprising a casing, a rotor mounted therein and a slidable liner surrounding said rotor for varying the displacement of said pump, a source of fluid under pressure, ducts for supplying fluid from said source to the spaces within said casing on opposite sides of said liner, a valve" for controlling said ducts comprising two cooperating movable parts, one of said valve parts being arranged to supply fluid to the space on one side of said liner when moved in one direction and to supply fluid to the space on the other side of the liner when moved in the opposite direction, and the said second movable part of said valve being connected to and movable with said liner and arranged to cut oif the supply of fluid when said liner reaches a predetermined position with respect to the first movable valve part, said valve part being movable in one direction from neutral position for forward operation and in the opposite direction from neutral position for reverse operation, means for normally maintaining said first valve part in neutral position, an engine for driving said drive shaft and provided with an accelerator, a connection for operating said first valve part in the direction for forward operation by movement of said accelerator from idling position in one direction, said connection'including means for at will reversing the direction of operation of said first valve part when said accelerator is moved from idling position in the same direction, and means responsive to increase in pressure in the fluid circuit of said primary pump for moditying the control'of said first valve part by said accelerator. OLOF LJUNGS'I'ROM. 

